It has been realized in the past that if an oxide is allowed to form on the surface of a semiconductor between the main body of the semiconductor and an etch mask, that there will be undercutting of the mask in the areas of the oxide and the semiconductor based material will be etched, where the desired action is a groove, to be wider than the mask area supposedly defining the width of the groove. Typically, any natural (naturally occurring as opposed to actively generated) oxides which are formed on the semiconductor are uneven in thickness or depth, and thus, the etched groove has varying amounts of undercutting and the groove width is not uniform. If the desired action is to have a mesa of a constant width as opposed to a groove, the same detrimental effects occur. In other words, the mesa is not as wide as the mask and the mesa is not uniform in its dimensions.
It has often been found in the past that, even though the semiconductor material is cleaned with a cleaning agent or solution such as hydrogen fluoride (HF) or sulfuric acid (H.sub.2 SO.sub.4), an uncontrolled amount of oxide is formed on the surface and in varying thicknesses between the base semiconductor and the mask as applied. One attempt to compensate for this problem is shown by a U.S. Pat. No. 4,595,454 in the name of Dautremont-Smith et al. The process described in the patent is to generate a prescribed thickness layer of oxide surface area in an oxygen rich atmosphere after the cleaning process, so that any naturally formed oxides are of a relatively small thickness, compared to the intentionally added oxide, and with this added oxide, the undercutting would be reasonably uniform.
The present method was formulated by the present inventor after a considerable amount of study revealed that the natural oxide was being formed accidentally by subjecting the semiconductor body to temperatures whereby oxides would form prior to the removal of oxygen from the environment in which the body was placed. This often occurred due to the placing of the semiconductor bodies in a plasma deposition system environment, whereby contact with the hot surfaces therein would immediately start forming oxides. These oxides may also form with time at room temperatures. (Typically, no more than ten minutes may be allowed to lapse between cleaning and the removal of an oxygen environment.) The thickness of the oxides formed depending upon various parameters, such as cleaning procedures, location of heat source and thermal conductivity of the semiconductor body before the environment within the furnace had been replaced by an oxygen-free atmosphere.
Thus the present invention comprises cleaning the surface of the semiconductor of all oxides (if any) at a temperature, such as room temperature, which will not result in the formation of any additional natural oxides. The body must quickly be placed in an atmosphere that is oxygen free (typically less than ten minutes). In other words, the environment is brought down to room temperature before the semiconductor bodies are placed therein and the evacuation of all the oxygen from the environment is performed before the temperature is raised.
It is thus an object of the present invention to provide an improved method of defining the topography of a semiconductor body through the use of etchant masks and etchants to improve the consistency and definition of grooves and mesas to be formed on the semiconductor surface.